Dub importPath and sourcePath variables

[Max via Digitalmars-d-learn]

Hello,

I am having a problem working with custom build types in Dub.
For my project, when I perform a regular build, all of my source 
code is contained in ./source or ~/.dub/packages/<package-name>.
However, I want to specify a custom build type (called 'tests') 
that imports modules from the additional directory ./tests.
Accordingly, my dub.json file is structured as follows:

{
        "name": "q1dcfd",
        "authors": [
                "Tom Reddell", "Viv Bone"
        ],
	"description" : "Quasi One Dimensional Compressible Flow 
Dynamics",
        "copyright"   : "Copyright © 2018, Tom Reddell",
        "license"     : "MIT",
        "targetType"  : "executable",
	"sourceFiles"         : ["$CPD/source/cpp_layer.o", 
"$CPD/source/libCoolProp.a"],
    "excludedSourceFiles" : ["source/experimental/*"],
        "dependencies": {
        "mir"           : "~>3.2.0",
        "mir-algorithm" : "~>3.4.14",
        "lubeck"        : "~>1.1.2",
                "coolprop"      : "*"
        },
    "buildTypes" : {
        "tests" : {
            "buildOptions"        : ["unittests", "debugMode"],
            "importPaths"         : ["tests/", "source/"],
            "sourcePaths"         : ["tests/", "source/"],
            "excludedSourceFiles" : ["source/experimental/*"]
        }
    }
}

When I manually assign my "importPaths" and "sourcePaths" 
variables during a "tests" build, I overwrite the values in these 
variables that have been automatically added due to my 
dependencies, causing the build to fail.
Is there a way that I can append "tests" to importPaths and 
sourcePaths, rather than overwriting them completely?

Regards,

Viv